Indexes are the objects that DBA uses them everyday and maintaining them very often, during the maintenance routines. The main purpose that we use the indexes is to retrieve data as fast as it possible.

Types of indexes are:

Cluster - max 1 per table & more about the structure.Non Cluster - max 999 per table & more about the structure.Unique - can contains also one NULL value!

There are many types of indexes that you can use them in different scenarios of your SQL Server databases environment. So the article covers Cluster, Non Cluster & Unique indexes that cannot created in a table or more exactly in which data type of the columns is not allowed to create indexes.